Preparation and characterization of tungsten oxide zirconia catalyst

Tungsten oxide-zirconia catalysts were prepared by drying of powdered Zr(OH)(4) with ammonium metatungstate aqueous solution followed by calcining in air at high temperature. The characterization of prepared catalysts was performed using Fourier transform infrared (FTIR), Raman, X-ray photoelectron spectroscopy (XPS) , X-ray diffraction (XRD) and Differential scanning calorimetry (DSC), and by the measurement of surface area. The addition of tungsten oxide up to 20 wt% to zirconia shifted the phase transition of ZrO2 from amorphous to tetragonal to higher temperature due to the interaction between tungsten oxide and zirconia, and the specific surface area and acidity of catalysts increased in proportion to the tungsten oxide content. Since the ZrO2 stabilizes supported tungsten oxide, for the samples equal to or less than 5 wt% tungsten oxide was well dispersed on the surface of zirconia, but for the samples containing 13 wt% or above 13 wt% the triclinic phase of WO3 was observed at any calcination temperature. Upon the addition of only small amount of tungsten oxide (1 wt% WO3) to ZrO2, both the acidity and acid strength of catalyst increased remarkably, showing the presence of Bronsted and Lewis acid sites on the surface of WO3/ZrO2. The high acid strength and large amount of acidity were responsible for the W=O bond nature of complex formed by the interaction between WO3 and ZrO2.